The present invention is generally concerned with mobile radiocommunication systems.
The present invention is more particularly concerned with power control used in such systems to improve performances (in terms of quality of service, of capacity, . . . etc.).
The present invention is in particular applicable to mobile radiocommunication systems of CDMA (xe2x80x9cCode Division Multiple Accessxe2x80x9d) type. In particular, the present invention is applicable to UMTS (xe2x80x9cUniversal Mobile Telecommunication Systemxe2x80x9d).
One type of power control which is used in CDMA systems is the so-called closed-loop power control.
The closed loop generally runs on a fast basis in order to adjust the transmission quality (generally represented by the SIR, or xe2x80x9cSignal-to-lnterference Ratioxe2x80x9d) around a transmission quality target value (generally a SIRtarget value), by sending appropriate power control commands back to the transmitter. The closed loop thus sends an xe2x80x9cupxe2x80x9d power control command back to the transmitter when the estimated SIR is below the SIRtarget value, or a xe2x80x9cdownxe2x80x9d power control command otherwise.
The SIRtarget value is generally adjusted by a so-called outer loop. The outer loop generally runs on a slower basis in order to adjust the quality of service (generally represented by the BER, or xe2x80x9cBit Error Ratexe2x80x9d, or the FER, or xe2x80x9cFrame Error Ratexe2x80x9d) around a quality of service target value (generally a BER or FER target value). The outer loop thus increases the SIRtarget value when an estimated BER or FER is above a BER or FER target value, or reduces it otherwise.
Such an implementation may lead to such situations where the SIRtarget value is needlessly increased, therefore needlessly increasing the interference level in the system.
This may in particular be the case under such conditions as when the transmitter has already reached its maximum transmit power, or when the system has become overloaded. In such a case the SIRtarget value is uselessly increased, while this cannot result in any quality improvement. This may not be considered as a drawback in itself, as long as such conditions apply, but the SIRtarget value may therefore reach a too high value, and, when such conditions no longer apply, this will result in setting the transmit power at a level higher than necessary, therefore needlessly increasing the interference level in the system, until the algorithm reaches a correct value again.
The outer loop is usually implemented at the receiver side, in order to reduce adaptation delays between quality measurements and SIRtarget setting However, the receiver may not have means to know why the quality of service cannot be maintained with the current SIRtarget value, and, as indicated above, may try to increase it, even though the current SIRtarget value cannot be reached due to network overload for instance.
Therefore there is a need to provide a power control method avoiding such drawbacks.
An object of the present invention is therefore a method for improving performances of a mobile radiocommunication system using a power control loop which controls power according to a transmission quality target value, and an adjustment process for adjusting said transmission quality target value, a method wherein said adjustment process is controlled based on an assessment of the convergence of said power control loop around said transmission quality target value.
According to another object of this invention, said control of said adjustment process includes not performing any adjustment, if said power control loop has not converged around said transmission quality target value.
According to another object of this invention, convergence of said power control loop is assessed by determining if a difference between an estimated average transmission quality and said transmission quality target value is within given margins.
According to another object of this invention, said margins are determined so as to take into account power control errors.
According to another object of this invention, said margins are optimised according to radio conditions.
According to another object of this invention, said margins are different depending on whether said adjustment requires increasing or reducing said transmission quality target value.
According to another object of this invention, said estimated average transmission transmission quality is estimated on an averaging period which is long enough to enable said power control loop to converge, but not too long to take into account fast changes in power control requirements.
According to another object of this invention, said averaging period is optimised according to radio conditions.
According to another object of this invention, convergence of said loop is assessed by determining if, among successive values representative of an estimated average transmission quality, at least one of these values is above said transmission quality target value and at least one of these values is below said transmission quality target value.
According to another object of this invention, said transmission quality is represented by a Signal-to-Interference Ratio (SIR).
According to another object of this invention, said adjustment process is an outer loop which adjusts a quality of service around a quality of service target value.
According to another object of the invention, said mobile radiocommunication system is of CDMA type.
According to another object of the invention, said power control is performed in on uplink transmission direction of said mobile radiocommunication system, using an uplink power control loop and an uplink adjustment process, and said uplink adjustment process is controlled, based on an assessement of the convergence of said uplink power control loop.
According to another object of the invention, said power control is performed in a downlink transmission direction of said mobile radiocommunication system, using a downlink power control loop and a downlink adjustment process, and said downlink adjustment process is controlled, based on an assessement of the convergence of said downlink power control loop.
The present invention also has for its object a mobile radiocommunication network for performing such a method, said mobile radiocommunication network comprising means for performing said uplink power control loop, means for performing said uplink adjustment process, and means for controlling said uplink adjustment process, based on an assessment of the convergence of said uplink power control loop.
According to another object of this invention, said mobile radiocommunication network is of the type comprising at least one base station, comprising means for performing said uplink power control loop, and at least one base station controller, comprising means for performing said uplink adjustment process.
According to another object of this invention, a base station of such a network comprises;
means for performing measurements necessary for the assessment of the convergence of said uplink power control loop,
means for sending such measurements to a base station controller.
According to another object of this invention, a base station controller of such a network comprises:
means for receiving such measurements from a base station,
means for assessing the convergence of said uplink power control loop, based on such measurements , and for controlling said uplink adjustment process, based on this assessment.
The present invention also has for its object a mobile station for performing such a method, said mobile station comprising means for performing said downlink power control loop, means for performing said downlink adjustment process, and means for controlling said downlink adjustment process, based on an assessment of the convergence of said downlink power control loop.
According to another object of this invention, such a mobile station comprises:
means for performing measurements necessary for the assessment of the convergence of said downlink power control loop,
means for assessing the convergence of said downlink power control loop, based on such measurements, and for controlling said downlink adjustment process, based on this assessment.
According to another object of this invention, such a mobile station further comprises means for receiving parameters required for said assessment of convergence of said downlink power control loop, from a mobile radiocommunication network.